In mobile communications, a multi-band wireless device can refer to a mobile phone (or other wireless communication equipment) that supports multiple radio frequency (RF) bands. Each RF band spans a range of radio frequencies and contains multiple radio frequency channels. Some multi-band mobile wireless devices may use a single carrier frequency for communication, whereas other multi-band mobile wireless devices may support multi-carrier communication using multiple frequency channels simultaneously. Support for multiple radio frequency bands in multi-band wireless devices provide for roaming between different regions of the world, where different wireless communication protocols can be used to provide mobile wireless services. For widely separated radio frequency bands, parallel transmit and receive signal path circuits may be required, which can increase the cost, physical size, complexity and power demand of multi-band wireless devices. Multi-band wireless communications can directly impact antenna design for the multi-band wireless devices that support such communication.
Fundamental elements of a radio system include a receiver, a transmitter, which in combination with the receiver can be referred to as a transceiver, and one or more antennas to radiate and receive radio waves. Characteristics of the antennas can be based on specifications for the receiver and the transmitter, for example a bandwidth and a carrier frequency. In some embodiments, the receiver and the transmitter can operate at the same carrier frequency such that an antenna in the wireless device may only require tuning to a single carrier frequency.
First generation (1G) mobile systems utilized a single carrier frequency for operation, e.g. in North American, the Advanced Mobile Phone System (AMPS) system used a carrier at 800 MHz. With the evolution to second generation (2G) standards, mobile systems (TDMA, GSM, CDMA) introduced dual radio frequency bands. Dual band mobile devices operate using two radio frequency bands. Thus, 2G mobile wireless devices, e.g., user equipment (UE) and network equipment such as a base transceiver station (BTS) can require a dual-band antenna apparatus for operation. A dual-band antenna apparatus for a mobile wireless device can be implemented using two separate antennas or can be implemented by combining multiple elements to create an antenna that operates in two separate radio frequency bands.
With the evolution of wireless communication standards, e.g. from 2G mobile systems to third generation (3G) mobile systems, and with the demand to provide wireless communication devices that can connect to wireless services worldwide, the complexity of antenna designs continue to increase. Multi-band mobile wireless devices have evolved from dual-band to tri-band to quad-band capabilities. For example, a quad-band wireless device can support four separate radio frequency bands, e.g., 850 and 1900 MHz radio frequency bands, typically used in the Americas (ITU region 2), and 900 and 1800 MHz radio frequency bands typically used in Europe and other regions. Some wireless communication devices that support 2G and 3G wireless communication protocols support all four radio frequency bands.
The evolution to LTE/4G (Long Term Evolution/4th Generation) wireless communication protocols requires mobile wireless devices to support many radio frequency bands. Additionally, for advanced capability wireless communications, there is an increasing demand for wireless systems to use multiple carrier frequencies simultaneously. This demand impacts both mobile wireless devices, e.g., UE's, and access network equipment, e.g., BTS's. Recent advances in wireless communication protocols (e.g., LTE-Advanced protocols) provide for carrier aggregation (CA) that can support simultaneous communication using up to five distinct radio frequency carriers to achieve wider bandwidth and higher throughput. In addition, Dual subscriber identity module (SIM) Dual Standby (DSDS) and/or Dual SIM Dual Access (DSDA) wireless communication devices can require transmission and/or reception using at least two frequency channels in parallel. The requirements of these applications can impose a significant challenge to the design of antennas for wireless communication devices, especially antenna tuning design. Therefore, there is a need for antennas that can operate in a multi-band multi-carrier environment and provide optimal performance across multiple radio frequency bands, while also meeting particular form factor and/or cost objectives.